Re: Retinal image size calculation for human eye.

From: andrew Judd (andrewedwardjudd_at_hotmail.com)
Date: 06/21/04 

Date: 21 Jun 2004 05:19:58 -0700

"Bruce Woodburn" <brucew@dccnet.com> wrote in message news:<10dcr82nec9h888@corp.supernews.com>...
> I don't know if this is going to help...
>
> Imagine you start with a normal eye that is in focus at distance. To convert
> it to a myopic eye, you put an imaginary plus sphere lens inside the eye at
> the plane of the natural lens, about 5.5 millimeters behind the cornea. To
> compensate, a minus spectacle lens is placed 14mm in front of the cornea.
> You now have a reversed Galilean Telescope (paired plus and minus lenses)
> which makes the image smaller. The opposite situation is true for hyperopes,
> who see a magnified image (about 2.5% for each diopter)
>
> When you look through a minus lens that is "too strong", your natural lens
> accommodates by becoming more plus. This increases the strength of the
> reversed Galilean Telescope and reduces the image size. It's not so much the
> minus lens that is making the image smaller as the accommodation of your
> lens. If accommodation is paralyzed with eye drops, the image would go
> blurry, but remain closer to the same size.
>
> I think the "2.5% per diopter" rule is pretty close for both minus and plus
> lenses.
>
> Bruce
>
> PS: A Galilean Telescope is a 2 lens telescope (plus objective, minus
> eyepiece) arrange so their focal points coincide. Magnification (or
> minification) is the ratio of their strength in diopters (e.g.: a +1 diopter
> objective and a -4 diopter eyepiece gives a 4 power scope.) This power
> calculation doesn't apply to the armchair experiment described here because
> of the complexity of the optical system.

This sounds pretty reasonable Bruce.

Thanks

Andrew

Relevant Pages

  • Re: High Myopia cures by rest methods
    ... that eye, reading the 10 line at 10 feet on the black chart. ... Author Information Introduction Helmholtz's Theory Of Accommodation ... Accommodation Methods For Treating Presbyopia Pictures Bibliography ... that states that the crystalline lens is under increased equatorial ...
    (sci.med.vision)
  • Re: EYE SURGERY FOR PRESBYOPIA ( NEAR VISION GLASSES REMOVAL)
    ... The mechanism of accommodation has been normalised by combination and ... Increase in length of the eye by 0.34mm preaccommodated to 0.88mm ... Shifting of anterior pole of the lens backwards in preaccommodated ... Decrease in the length of posterior pole of the lens. ...
    (sci.med.vision)
  • Establishing Depth-of-Field at 0.3 Diopters.
    ... The "Helmholtz" theory (pure lens accommodation) versus the ... Technical Analysis of the concept of the dynamic eye. ... COMPARISON OF DEPTH OF FOCUS BETWEEN SPECTACLE AND CONTACT LENS ...
    (sci.med.vision)
  • Re: EYE SURGERY FOR PRESBYOPIA ( NEAR VISION GLASSES REMOVAL)
    ... you still will develop a condition called presbyopia as you ... Delhi claims so far no where in India such an eye surgery is performed ... brought about by lens, zonules and ciliary body muscle of the eye. ... from presbyopia or the deficiency of accommodation. ...
    (sci.med.vision)
  • Re: Tell me about accomodation after cataract surgery
    ... No, but the artificial lens will have no focusing ability, as it will be ... Your ciliary muscle will continue to constrict, ... Eye: Structure and Function" where he said, in effect, that the ... ciliary ennervation never stops in presbyopia; only the accommodation ...
    (sci.med.vision)